An energy absorbing member that absorbs impact energy is used around a seat of an airplane, around a seat of a vehicle, around a bumper, and in each structural member (see, for example, Japanese Patent Application Laid-open Publication No. S60-109630 and Japanese Patent Application Laid-open Publication No. S62-17438). Since it necessitates that the energy absorbing member is light and has high rigidity apart from having a capability to absorb the impact energy, a composite material of a resin and a reinforced fiber, so called fiber reinforced plastic (FRP), especially carbon fiber reinforced plastic (CFRP) is suitable. In such energy absorbing member, an energy absorbing mechanism in which a local failure is caused to occur in a certain part of the energy absorbing member, such as an edge of the member as a starting point, and energy is absorbed by using this local failure, can be considered.
Moreover, regarding an impact resistance in a vehicle, mainly a frontal impact accident is apprehended, and as a measure against this, a member called as a front side member made of steel is disposed in a hood, and energy is absorbed by crushing of the member upon the frontal impact accident.
On the other hand, in a helicopter, an impact due to a forced landing is apprehended, and as a measure against it the impact resistant material is disposed under a floor. However, as compared to a length of the hood of the vehicle, in a structure under the floor of the helicopter, the height is limited for ensuring clearance under the floor. Furthermore, in recent years, since a need for a fuel tank under the floor becomes high for ensuring a cabin capacity, a restriction of an area and a stroke for disposing the impact resistant member is strict. Therefore, energy absorption efficiency higher than ever before is desired.
For this reason, so far, as an energy absorbing member, in a laminated composite material in which fibers are laminated, upon evaluating an effect due to a fiber material or a fiber orientation, for suppressing a peak of an initial load, providing an initiator that becomes a starting point for the destruction to occur has been proposed (see, for example, Japanese Patent Application Laid-open Publication No. H6-300068, Japanese Patent Application Laid-open Publication No. H6-341477, and Japanese Patent Application Laid-open Publication No. H7-217689). Whereas, in a composite structure of resin and fiber, to improve an out-of-plane strength (peel strength) including a shearing strength between layers and of a composition plane, a textile substrate for the composite material that uses needling has been proposed (see, for example, Japanese Patent Application Laid-open Publication No. 2003-39429).